The present invention relates to a light measuring system useful in determining the proper exposure in a photographic device such as a camera, a printer of photographic papers and the like or useful in measuring the average intensity of light incident to a device in which the light is utilized for the operation thereof.
Heretofore, a number of light measuring systems have been developed. However, almost all such systems incorporate analogue circuits therein so that the accuracy in the measurement of light, the range of the measurement of various intensity of the light, the capability of adjustment in various operations of the device and operational functions are insufficient and render the constructions to be complicated and expensive when the performance of the device is to be improved.
Further, in the prior art light measuring system, a single capacitor is usually used for charging or discharging the electric charge charged therein by a current from a photoelectric element which receives the light so as to generate the current indicative of the intensity thereof in order to measure the intensity of the light. In such a system, the accuracy of the measurement is deteriorated if the intensity of the light is low with respect to the capacity of the capacitor, while the accurate measurement of a high intensity of the light is made impossible if a capacitor used is of a small capacity because of the saturation of the charged voltage.
In order to broaden the range of measurement of the light having widely variable intensity, methods for performing logarithmic compression and expansion of the intensity of light have also been proposed. However, such logarithmic compression and expansion methods for measuring the intensity of light have led to deterioration in the accuracy of the measurement.
The present invention aims at avoiding the above described disadvantages of the prior art light measuring systems.